Reversing valve



Nov. 7, 1961 A. R. wAsHBURN E'AL 3,007,451

REVERSING VALVE Filed May 5, 1960 v s sheets-sneet 1 Vn O @.2 l

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Nov. 7, 1961 A. R. WASHBURN ETAL 3,007,451

REVERSING VALVE Filed May 3, 1960 3 Sheets-Sheet 2 I ce? ,.100 n f 64"'Q/ a .1% 154166 /f Nov. 7, 1961 REVERSING VALVE Filed May 5, 1960 A.R. WASHBURN ET AL 3 SheetsSheet 5 214 217 if ya zw United States PatentO REVERSING VALVEl Arthur R. Washburn, Anaheim, and Robert W. Reekstir;

West Covina, Calif., assignors, by mesne assignments,

to Dynaquip, Long Beach, Calif., a corporation of Califoma Filed May 3,1960, Ser. No. 26,475 14 Claims. (Cl. 121-150) The present inventionrelates in general to reversing valves for use in hydraulic pressuresystems, and more particularly to a reversing valve adapted'for use inconnection with hydraulic reciprocating motors in such systems.

The reversing valve of the inventionV has a particularly usefulapplication with hydraulic pumping jacks of the type used to actuateproduction pumps in oil wells. Therefore, the invention will bedescribed in that environment. However, it will be understood that thereare other useful applications, and that the detailed description of thisone is not intended to be limitative.

In the illustrative systems to be described herein, a reciproacting pumpis positioned within the production zone of an oil well and arranged topump oil to the surface through a tubing string. The pump is actuatedfrom the ice 2. thatjoins the power' cylinder, to move back to its rstoperating position, .whereiniluid'l isi again introduced to thepowercylinderlt initiate another power stroke 'I'heelminationv ofthepilotvalve in`th'e-improvedias-l sembly' ofthe" present invention ismosti advantageous# in that it simplifies the construction of thevalveitself, and

surface by a sucker rod, which in turn is reciprocated Iby a pumpingjack.

The aforementioned pumping jack, embodying a power cylinder and a powerpiston, is normally connected into a hydraulic pressure system whichtypically includes a reservoir and a power pump. The power pumpintroduces iiuid to the cylinder to drivev the piston upwardly inV apower stroke. At the end of the power stroke, hydraulic iuid is releasedfrom the cylinder so that-the piston may return `to its lower positionin a return stroke. `During the return stroke, liuid from thepower pumpis bypassed directly to the reservoir. The piston is coupled by suit-.able means to the string of sucker rods so that reciprocal motion isimparted to actuate the production pump down in the well. v

A reversing valve is provided in the above-described hydraulic pressuresystem to automatically control the operation of the pumping jack. Thevalve is controlled to have 'a iirst operating position wherein itpermits hyfdraulic iiuid from the power pump to 'be introduced to thecylinder to drive the piston in the power stroke. At vthe end of thepower stroke, the valve is moved to a second operatingA position whereinhydraulic iluid is released .from the cylinder and the piston makes thereturn stroke. p In the past, a pilot valve, actu-ated in response tothe position of the power piston in its cylinder, has been utilized tocontrol the operation of Ithe reversing valve. Thus in eiect, two valveshave been required to automatically control the operation of the pumpingjack.

It is a primary object of the present invention to pro- Avide areversing valve ofthetype described which obviates the need for aseparate pilot valve.

In accordance with the improved structural concepts .of the invention, asingle valving member 'or spool in the Vreversing valve is itself madeto respond to fluid pressure ported from the main power cylinder. In theparticular embodiment shown herein, the spool is normally urged to a rstoperating position, during the power stroke. At the end of the powerstroke,a plunger on the spool of the reversing valve is cau-sed torespond directly. to the liuid pressure on the pressure side of thepower piston acting through an upper pressure-sensing conduit. Thisfluid pressure moves the spool-to it-s second operating position,wherein fluid is released from the power cylinder so that the powerpiston moves through its return stroke. At' the end of the returnstroke, .the spool responds to the depressurizing of a secondpressure-sensing conduit in that it reduces the number of componentparts re*` quired in the valve assembly to enable it to perform itsintended function.

In addition, the improved construction of the present inventionreducesthe number of conduits or pipelines and joints required to fluidcouple the improved valve of the invention into the hydraulic system, ascompared with the number of such elements required to couple the priorart type of valves into the hydraulic system. This reduction in thenumber of conduits yand joints is highly desirable, especially for iieldinstallations.

It will be appreciated that a tremendous force is exerted on thepowerpiston by the weigh-t of the sucker rods. Because of this force, it isusually necessary that some resistance or throttling effect jbe providedto control the speed of the return stroke of the power piston.

A somewhat related `problem'is also encountered during the returnstroke. If some throttling or resistance vis not provided in the bypass,the power pump will be caused to speed up excessively or race andtheduid pressure acting on the' v'anes and seals of the pump will begreatlyreduced. Surges of pressure on the pump are undesirable' as they causeexcessive wear.

It is, therefore, a further object of they invention to provide animproved reversing valve which incorporates adjustable means forcontrolling the speed of the return stroke of the power piston and forcontrolling the load on the powerV pump during the return stroke.

AAnother object is to provide a reversing valve embodying means forpreventing dead centering and hunting of the power piston in itscylinder adjacent the ends of the power and return strokes.

Still -another object of the invention is to provide a reversing valveof the type described which is sturdy and durable in its constructionand which is capable of handling extremely high iluid pressures.

The objectsand advantages of this invention discussed above will bebetter understood, and other objects and advantages will become apparentby a consideration of the following detailed description when taken inconjunction with the accompanying drawings, in which:

FIGURE 1 is a side elevational view of a typical hydraulic'pressuresysternof the type described, which incorporates the reversing valve ofthe invention;

FIGURE 2 is a fragmentary elevational view of the system of FIGURE l onan enlarged scale and partly in section to reveal the internal operatingcomponents of the pumping jack and of the reversing valve, the valvebeing illustrated in arst position for the power stroke;

FIGURE 3 is a sectional view of the reversing valve of FIGURE 2, on .anenlarged scale, and illustrating the valve in a second operatingposition for the return stroke;

FIGURE 3a is a fragmentary section view of the assembly of FIGURE 3taken along the line 3ra-3a of that figure;

FIGURE 4 is an enlarged side elevational view of a modified form of lthereversing valve of the invention;

FIGURE 5 is a sectional view of the modified reversing valve of FIGURE4, illustrating the various operatp. ing components which areincorporated in the body of the valve, and showing these components inthe iirst operating position of the valve;

`FIGURE 6 is a sectional view similar to the view of FIGURE S butshowingv the operating components of the valve in the second operatingposition; and

FIGURE 7 is a broken sectional view taken on the line 7-7 of FIGURE 4.

The duid-actuated pumping jack illustrated in FIGURE l includes a powercylinder 10, which is supported in a vertical position by a pair ofpedestals 12 and 14. These pedestals, as described and claimed incopending application, Serial No. 10,302, are cylindrically shaped andeach defines an inner chamber which is used as a reservoir and coolingchamber for the iluid circulating in the system.

The power cylinder is mounted on a support member 16 which, in turn, issupported by the upper ends of the pedestals 12 and 14. The assembly ofFIGURE l also includes a lower support member 18, which is attached tothe lower ends of the pedestals 12 and 14. The lower support member 18is mounted on the upper end of a well tubing 20, which extends down intothe well and forms an enclosure for the sucker rod string (not shown)and for carrying production uid from the well.

As shown in FIGURE 2, the vertically extending power cylinder 10 isclosed at its lower end by member 34, which incorporates an integralstuing box 36. The base member 34 is secured to the support member 16referred to above.

Slidably mounted within the power cylinder 10 is a power piston 40,which is adapted to reciprocate therein between upper and lower limitingpositions in a power and a return stroke.

In order to impart reciprocal motion to the production pump down in thewell, the power piston 40 is mechanically coupled to the pump. Couplingis etected bysecuring the piston 40 to a piston rod 44 by means of aclamp 42, and then, in turn, joining the piston rod to the string ofsucker rods. The pressure-sealing of the power cylinder 10 is maintainedby extending the piston rod out of the cylinder through a pair ofpacking glands 35a and 35b in the stuthng box 36 and by suitably closingthe top of the cylinder as with a cap 38.

The interior of the cap 38 is coupled to the top of the pedestal 12 byscavenging conduit 39. The conduit 39 carries fluid from the powercylinder 10 on the upper side of the piston 40 back to the system.Similarly, an auxiliary scavenging conduit 39a extends from the stuingbox 36 to the conduit 39, so that any uid leaking through the upperpacking gland 35a and accumulating in the stung box 36 will also becarried back to the pedestal 12. Fluid pressure for reciprocating thepower piston 40 in its cylinder 10 is supplied through a series ofconduits by a power pump 22, preferably driven by an electric motor 23.A reversing valve 25, which incorporates the concepts of the presentinvention, is installed in the conduits intermediate the pump 22 andythe power cylinder 10 to automatically control the operation of thepower piston 40 in its cylinder.

In operation, the power pump 22 draws uid from the lower end of thereservoir-pedestal 14 through conduits 26 and 30. In the illustratedpressure system a valve 32 is installed in the conduit 26 and a filter28 is installed intermediate conduits 26 and 30. Outlet Huid from thepump 22 passes into the reversing valve 25 of the invention 4through aconduit 24. The reversing valve 25 is operable to alternately port fluidto the power cylinder 10 through a conduit 64 or to the pedestal 12through a bypass and return conduit 66.

As will later be described in detail, when the reversing valve 25 is inits rst operating position, fluid is introduced through conduit 64 tothe power cylinder 10` to move the piston 40 up in a power stroke. Whenthe valve is in its second operating position, fluid is released fromthe cylinder 10, and the piston 40 will move down in a return stroke.Return fluid from the cylinder flows back to the reversing valve 25through the conduit 64 and, thence, is ported to the bypass and returnconduit 66, which in turn is coupled to the pedestal 12.

With reference to FIGURE 2, the conduit 66 is coupled to the interior ofthe pedestal 12 at an intermediate point in accordance with ltheteachings of the aforementioned copending application. During the returnstroke of the power piston 40 in its cylinder 1G, 'return hydraulicfluid and the uid continually' being circulated by the pumpf22 enter theinterior of pedestal 12 through the conduit 66. This duid is circulatedthrough the` interiors of pedestals 12 and 14, which act as reservoirsbeing intercoupled by an upper conduit 76 and a lower conduit 70. Aspreviouslynoted, the inlet fluid to the circulating pump 22 is drawn offpedestal 14 near the lower end thereof.

The reversing valve 25 includes a body 150 having an internalcyclindrical chamber 152 with a spool 154 slidably mounted therein.Reciprocal movement of the spool 154 inthe chamber 152 between the firstoperating position to the left in the chamber, as illustrated in FIGURE2, and the second operating positon to the right in the chamber, asillustrated in FIGURE 3, controls the ow of hydraulic fluid to and fromthe power cylinder 10 in the manner' previously explained. Such movementof the spool also effects the bypassing of the pressurized fluid fromthe power pump 22, as will be described.

The spool 154 has a longitudinal bore 156 extending into one end andanother longitudinal bore 164 extending into the opposite end. To effecta valving action,

' the spool 154 is formed with a pair of cylindrical lands or members158 and 160 on its opposite ends, which lands or members engage thecylindrical wall of chamber 152 in a close sliding t and thereby act asplungers.

A compression spring 168 positioned in the bore 164 bears against thespool 154 and against a disc-like plug 170 to normally urge the spool tothe left to its rst operating (power stroke) position in the chamber152. The plug 170 has an O-ring sealing member 172 in its pe- -riphery,which engages the wall of chamber 152 to hermetically close the chamber.

The body is tted with a first end cap 174, which is secured in theright-hand end of the body -by any appropriate means. The assembly alsoincludes a second end cap 178, which is secured to the opposite end ofther body. A pair of gaskets 176 and 180 are interposed between end caps174 and 178, respectively, and the vbody 150.

Throttling of the return uid from the power cylinder 10 is accomplishedby Iadjusting the limit position of the spool 154. To this end, a setscrew 182 in the right-hand end cap 174 provides means for suitablyadjusting the second operating position of the spool 154 in the chamber152. The set screw 182 is threaded into the end cap 174 and bearsagainst plug 170. Adjustment of the screw 182 varies the relativelongitudinal position of plug in chamber 152 and thereby controls thelimit position of the spool 154 when it is moved to the right to itssecond operating position shown in FIGURE 3. A lock nut 184 is threadedon the set screw 182 to serve as locking means for the screw.

An inlet port 186 formed in the body 150 extends radially downward fromthe chamber 152 to connect with the conduit 24. A cylinder or outletport 188 extends upward from the chamber 152 in radial alignment withthe port 186 to connect with the conduit 64. A return port 190 extendsradially from the chamber 152 at right angles to the axis of the ports186 and 188 and joins with the conduit 66. The return port 190 islongitudinally displaced from ports 186 and 188 to the left in chamber152. As may be seen in FIGURE 3a, the wall of the chamber 152 isundercut at 186a adjacent the two aligned ports 186 and 188 so that flowbetween these ports is never blocked, irrespective of the position ofthe spool 154.

The throttling of the fluid entering the valve during the return strokeof the power piston 40 is effected by a tapered end 192 -at the innerextremity of the land 160. This tapered end 192 extends into athrottling relationship with the edge of the undercut 186a when thespool 154 is in the second operating position shown -in FIG- URE 3. Itwill 4be noted that the -iiuid entering the valve from both the inletport 186 and the outlet port will be throttled when the spool is in thesecond operating position. The extent of such throttling may be suitablycontrolled by adjusting the longitudinal position of the plug 170 in thechamber 152 with screw 182 as described above. Pressurized control iiuidintroduced to one end of chamber 152 through a holding control port orconnection 196 and a starting control port or connection 198 is utilizedto move the spool 154 against the action of the spring 168 to its secondoperating position and to hold it there during the return stroke. Ineffect, 'an actuator is provided having an expansible chamber with apressure-responsive, movable wall therein, the wall comprising the lefthand end face of the land 158 on the spool. Such control fluid issupplied to the expansible chamber of the actuator by a pair ofpressure-sensing conduits 100 and 104 that connect to the ports 196 and198, respectively, and to the power cylinder at vertically spacedlevels.

A novel starting and holding action of the valve is accomplished bylocating the two ports 196 and 198 at slightly different points in thechamber 152. The holding control port 196 is located in the body 1 50slightly inwardly of the left-hand end thereof and communicates with anannular groove or recess 197 formed in the wall of the chamber 152. Thestarting control port 198 is formed in the end cap 178 and communicateswith the extreme left-hand end of chamber 152. A check valve 199 isprovided in the control port 198 to permit iiuid to enter the chamber152 through the port but not to escape through that port.

The lower sensing conduit 100 joins the power cylinder 10 adjacent thelower'limit of piston travel and at a level slightly above the junctionof the conduit 64 with the cylinder. The vertical spacing between therespective junctions of the conduits 64 and 100 must be at leastslightly greater than the length of the power piston 40, so that thepiston can slide below the opening to the pressure-sensing conduit 100without blocking the opening to the conduit 64.

The upper pressure-sensing conduit 104 joins the power cylinder 10 nearits upper end. The conduit 104 must be spaced a suicient distance belowthe cap 38 to allow the power piston 40 to move above the opening tothis conduit.

In describing a cycle of operation of the power piston 40 in thecylinder 10, the cycle will be assumed to commence with the spool 154 of-reversing valve 25 in its first operating position, being so urged bythe spring 168. Pressurized uid is pumped by the Power pump 22 throughthe conduit 24 to the inlet port 186 in the reversing valve 25. The land160 on the spool 154 blocks the flow of fluid to the annular space 163and, hence, to the return port 190. However, the undercut 186a (FIGURE3a) provides constant communication between inlet port 186 and valveoutlet port 188. Thus, liuid flows to valve outlet port 188 and throughthe conduit 64 to the lower end of the power cylinder 10.

The pressurized lluid entering the lower end of the power cylinder 10acts on the underside of the power piston 40, causing it to rise in apower stroke. When the power piston moves from the lowermost position,shown in full lines in FIGURE 2, above the opening to the lowerpressure-sensing conduit 100, pressurized fluid enters the conduit andflows to the holding port 196 and the annular groove 197. However, asmay be seen in FIGURE 2, the land 158 blocks the opening to the annulargroove 197 so that uid flow to chamber 152 is temporarily prevented.Therefore, the spool 154 remains in the position illustrated in FIGURE 2and the power piston 40 continues the power stroke inthe cylinder 10.

When the power piston 40 moves above the Yopening to the upperpressure-sensing conduit 104, as shown" in phantom lines in FIGURE 2,fluid enters the conduit. This pressurized fluid from the lower side ofthe powerpiston is ported to the end of the chamber 152'through thestarting port 198 having the check valve 199 therein. The land 158functions as a plunger and uid pressure acting on the left-hand end ofthe'spool 154 is sufiicient to move the spool .to the right in thechamber 152 against the resistance of the spring 168. As the left` endof the land 158 moves to the right of the annulargroove 197, whichcommunicates with the holding port 196, additional communication betweenthe chamber 152 and the power cylinder 10 is provided through the lowerpressure-sensing conduit 100. Y The spool will then be urged by thepressurized fluid from both sensing conduits 100 and 104 to its secondoperating position, illustrated in FIGURE 3. As previously described,the position of they spool 154 relative to the chamber 152 in its secondoperating position will be determined by the longitudinal position ofthe plug lrelative to the chamber 152. Y

In this second operating position,both the inlet port 186 and the outletport 188 are in communication with the return port 190 through theannular space 163 between the lands 158 and 160. Since iuid pressure inVthe reservoir-interior of the pedestal 12 is less than that in the powercylinder 10 below the piston 40, iiuid flows back through the conduit 64and the outlet port 188 to the valve 25. This return fluid is ported outthrough the return port 190 and ows through the conduit 66 back to thepedestal 12.

The resultant release of the hydraulic iluid from the power cylinder 10beneath the piston 40 permits the weight of the sucker rods and theproduction fluid'to lower the piston, thereby forcing the liuid inthe-power cylinder back to thel pedestal 12 through the aforementionedpath. Likewise, during the return stroke, the pressurized fluidcontinually being introduced by the power pump to thevalve 25 throughthe inlet port 186 also passes to the 4return port 190 and back to thepedestal 12.

As previously noted, the position of the spool 154 in its secondoperating condition is controlled by the plug 170, so that the taperedportion 192 on the land 160 provides a throttling effect on thehydraulic iiuid passing to the return port 190 from both the inlet port186 and the oulet port 188. This throttling effect serves two functions.One is to limit the speed with which the power piston 40 moves inthereturn stroke, and the other is to maintain at least a partial load onthe power pump 22 during the returnstroke. The latter function is toprevent excessive speeding up or racing of the pump 22, and to preventsurges of pressure from acting on the vanes 'and seals of the pump.

Previous pumping jack systems frequently have the problem of deadcentering or hunting of the'power piston in its cylinder. This situationis particularly likely to occur at the end of the power stroke. Usingthe present system as an example, as the power piston moves justslightly above the opening of the upper pressure-sensing conduit 104, soas to just crack open the inlet to the conduit, some pressurized controlfluidis delivered to shift the valve to its second operating or openposition. In past systems, this fluid is frequently suicient to justslightly open the valve. Under such conditions, the power piston ofprevious systems cornes to rest or dead centers in this position, orbegins oscillating or hunting about the inlet to the conduit 104. Deadcentering is caused by fluid being delivered to the cylinder by thepower pump at a rate which just balances that escaping through 4theslightly opened valve.

Hunting is caused by a small quantity of fluid be ing exhausted from thepower cylinder 10 through the valve, so that the piston 40 drops toblock the opening to the conduit 104. Because of the nature of previoushydraulic valves and pressure actuators therefor, the control fluidinitially delivered to the valve is not sufficient to hold it open.Hence, the valve closes and the piston s driven upwardly to again crackopen the inlet to the conduit 104.

In order to prevent the above-described dead centering and hunting, thespool 154 of the present invention is so proportioned relative to thespacing of aligned ports 186 and 188, and annular groove 197, that theleft end of the land 15'8 moves to the right of the annular groovebefore the land 160 unblocks the opening to the ports, i.e.,communication with the lower pressure-sensing conduit 100 establishedbefore the reversing valve opens.

Pressurized control fluid delivered by the lower pressure-sensingconduit 100 enters the chamber 152 before the valve is opened. rlfhus,the piston 40 continues to move in the power stroke as control iluidinitially enters the chamber 152 through the annular `groove 197,` and,hence, the possibility of dead centering of the power piston at thetermination of the power stroke is essentially removed.

Continuing the cycle of operation, as 'the power piston 40 d ropsr inthe cylinder 10, it lirst blocks the pressurized Huid in the cylinder 10from the entrance to the upper pressure-sensing conduit 104, so that thesupply of pressurized fluid to the chamber 152 through the starting port198 is removed. Further downward movement of the power piston 40 opensthe conduit 104 to the substantially atmospheric pressure in thecylinder Y10 above the piston. However, the check valve 199 preventscontrol uid from being returned Ifrom the chamber 152 through theconduit 104, so that the spool 154 remains essentially in the positionof FIGURE 3. Therefore, the power piston 40 continues its return strokewith the cylinder 10 on the lower side of the piston being in constantcommunication with the chamber 152 through the lower pressure-sensingconduit 100. This last-mentioned communication is necessary in order tohold the spool 154 in its second operating position in the chamber 152.

When the power piston 40 reaches and moves below the entrance to thelower pressure-sensing conduit 100, the pressure source is removed andthe fluid pressure urging the spool 154 against the action of the springis relieved to the essentially atmospheric pressure in the cylinder 10above the piston 40. The spring 168 then urges the spool 154 back towardits first operating posi-` tion and a quantity of the control fluid inthe chamber 152 is exhausted through the holding port 196 and conduit100 to the cylinder 10.

Due to the previously described proportioning of the spool 154, relativeto the spacing of the ports 186 and 188 and the annular groove 197,slightly before the land 158 moves over the annular groove 197, theother land 160 blocks the communication of the inlet and outlet portswith the return port 190, i.e., closes the reversing valve. Thus, lluidagain flows from the inlet port 186 through the undercut 18661 to theoutlet port 188 and is introduced to the power cylinder 10 on the lowerside of the piston 40 to initiate anot-her power stroke.

It will be appreciated that the land -158 must completely block theannular groove 197 before the piston 40 moves above the opening to thelower pressure-sensing conduit 100. If such blocking did not occur,control fluid would enter the chamber 152 and open the reversing valve,and the piston 40 would merely oscillate or hunt in short strokes aboveand below the opening to the conduit 100. To obviate hunting arestricted passage 162 communicates with the bore y156 and the annularspace 163 to bleed off control lluid trapped in the end olf chamber 152.As previously noted, control tluid is exhausted through the annulargroove 197 until said groove is nearly blocked by the land y158. Therestricted passage 162 must be of a size to bleed off suicient fluid sothat vthe annular groove vis completely blocked before the piston movesabove the opening to the lower circuit 100. The passage 162 continues tobleed olf the trapped Huid during the power stroke, allowing the spool154 to settle back to its first operating position.

Closing of the reversing valve commences the next power stroke and asthe power piston 40 moves up the cylinder 10, control lluid 4which wasexhausted to the upper side of the power piston 40 at the termination ofprevious return strokes will be carried up the cylinder and forced outthrough the scavenging conduit 39 back to the pedestal 12.

The reversing valve 25 also embodies means for relieving excessivepressure in the hydraulic system. This means includes a valve ball 202on a seat 204 to normally close an alternate passageway between theinlet port 186 and the return port 190. The alternate passageway isformed by a pair of intersecting ports 206 and 218, the port 206communicating with the inlet port 186 and the port 218 communicatingwith the annular space 163 in chamber 152.

A compression spring 212 and abutment 210 are provided to act on, andnormally urge the ball 202 to the seated position. A retainer 216 screwthreaded into a bore200 in the body serves to maintain the seat 204 inproper assembly when the ball is moved olf the seat by excessive tluidpressure.

The opposite end of the spring 212 bears on a spring anchor 214 which islongitudinally adjustable in the bore 200. Relative adjustment of theanchor 214 in the bore 200 varies the compression of the spring 212 and,hence, the force urging the ball 202 against the seat 204. An O-ring 217is disposed in a peripheral groove in the anchor 214 for sealingpurposes.

The means for adjusting the anchor 214 relative to the bore 200com-prises a set screw 220 threaded into the end cap 178 and bearingagainst the anchor 214. A lock nut 222 is preferably provided to retainthe screw in adjusted position.

When the pressure in the inlet port 186 exceeds a predetermined safelevel, the ball will be moved off the seat 204. Fluid will then owthrough the ports 206 and 218 to the return port 190. As the pressuresubsides to normal, the spring 21-2 will urge the ball 202 back againstthe seat 204.

In the embodiment of the invention illustrated in FIGURES 2 and 3, thetapered portion 192 of the land serves to simultaneously throttle boththe uid entering the valve 25 from the power pump 22 and the tluidexhausted through the valve from the cylinder 10 during the returnstroke of the piston 40.

Another embodiment of the invention, illustrated in FIGURES 4-7, issimilar to the rst embodiment except that separate and individuallyadjustable throttles are provided. One throttle is provided for thelluid entering the valve from the power pump 22, and the other is forthe uid exhausting through the valve 25 from the cylinder 10. The latterarrangement is advantageous in that it provides separate and independentmeans for adjusting the load on the pump 22 during the return stroke ofthe piston 40 and for adjusting the rate of the return stroke of thepiston.

Referring now to FIGURES 4-7, a main valve body 300is formed with aninternal cylindrical chamber 302.

4Slidably mounted within the chamber 302 is a spool 304, which isadapted to move between first and second operating positions to controlthe flow of tluid to and from the power cylinder 10 as in the previouslydescribed embodiment. An inlet port 306 is formed in the body andlongitudinally offset along chamber 302 is an outlet port 308. As shownin FIGURE 4, a reutrn port 310 is also provided in the body 300. Theseports correspond generally to the ports 186, 188 and 190 of the rsternbodiment of the valve and are adapted to connect to correspondingconduits of the hydraulic pressure system of ,FIGURE l. Since there isthis similarity, the Connecasomar 9 tion of this second embodiment ofthe valve in the hydraulic system will not be discussed again.

The body 300 is sealed at its opposite ends by a pair of end caps 312and 313 joined to the body 300 as with bolts 314. Suitable gaskets 320and 322 are interposed between the end caps 312 and 313-, respectively,and the body 300.

To prevent dead centering and hunting and to penmit complete return toits iirst operating position, the spool 304 must provide a bleed passageas in the iirst embodiment. To this end, the spool 304 has an axial bore332 extending into the right-hand end, as viewed in FIGURES and 6.Adjacent the central portion of the spool 304, a reduced axial bore 334joins the bore' 332 and extends nearly to the opposite end of the spool304. A restricted passage 336 extends from the reduced bore 334 to theopposite end of the spool 304. The spool 304 also has a restrictedlateral passage 338 extending from the reduced bore 334 to an annularspace 339 in the chamber 302. Thus, communication is provided from theend of chamber 302 to the annular-space 339 through the passage formedby restricted passage 336, bore 334, and restricted passage 339. A

A compression spring 316 normally urges the spool 304 to the firstoperating position in the chamber as illustrated in FIGURE 5. The spring316 bears against the end cap 313 and extends into the bore 332 to abuta shoulder 331 formed at the junction of the bores 332 and 334. l

The spool 304 is formed with a pair of lands 350 and 360 on the oppositeends thereof. In this embodiment, an additional land 352 is formed at anintermediate point on the spool 304. In order to control the ow of uidthrough the valve, the lands 352 'and 360 cooperate with a pair ofannular recesses 356 and 362 formed in the wall of the chamber 302.

Al iiuid passage from the annular recesses 356 and 362 to the returnport 310 is provided by a common manifold 374, shown in phantom lines inFIGURE 4 and partly in section in FIGURE 7. A pair of independentlythrottled connecting ports 375 and 375a join the recesses 356 and 362,respectively, to the manifold 374.

When the spool 304 is in the first operating position (power stroke),illustrated in FIGURE 5, the lands 352 and 360 block the iiow of iluidfrom inlet and outlet ports 306 and 308 to the annular recesses 356 and362, i.e., the reversing valve is closed. However, when the spool 304 isin this position, passage is provided from the inlet port 306 to theoutlet port 308 through an annular space 361 in chamber 302 intermediatethe lands 352 and 360. Thus, iiuid introduced to the inlet port 306 bythe power pump 22 flows to the outlet port 308, but is blocked from thereturn port 310. As previously described, this fluid flows to the powercylinder 10 to drive the power piston 40 in a power stroke.

When the spool 304 is in the second operating position (return stroke),illustrated in FIGURE 6, passage is provided from the inlet port 306 tothe annular recess'362, and from the outlet port 308 to the annularrecess 356. Thus, in this condition, both the inlet port 306 and theoutlet port 308 are in communication with the return port 310. However,such communication is through separate paths to the manifold 374, whichin turn connects to the return port 310. v

In order to separately throttle the iluid flow from both the powercylinder 10 and the power pump 22 during the return stroke of the powerpiston 40, identical but independent throttles 370 and 37011 areinstalled in the body 300. These throttles provide adjustable means forcontrolling the fluid flow between the annular recesses 356 and 362,respectively, and the manifold 374. Since the two throttles areidentical, only the unit 370 will be described in detail, it beingunderstood that the same description applies to the unit 370a.

Referring to FIGURE 7, the throttle 370 comprises a valve 376cooperating with the opening of the connecting port 375 to the manifold3-'74 to define a restricted passage. The valve 376 is supported by aretaining sleeve 378, which in turn is threaded into the body 300.Sealing between thev valve 376 and the sleeve is obtained by instailingan O-ring 380 in a circumferential groove in the valve, the O-ring 380being adapted to sealingly engage the inner periphery of the sleeve 378.

The opening of the port 375 to the manifold 374 is slightly enlarged andbeveled to provide a tapered seat 377. The valve 376 is formed with acorrespondingly tapered head 379, such that when the valve is adjustedinwardly toward the port 375, the area of the passage between thetapered head 379 and the seat 377 is reduced. Conversely, as the valve376 is backed away from the port 375, the area of the passage, ofcourse, is increased.

The valve 376 is formed with a threaded extension 383, which extendsthrough a threaded portion of the retainer 378. A lock nut 382 isutilized to maintain the valve in adjusted position.

It is evident that the throttle 370 provides adjustable means forthrottling the uid flow between the annular recess 356 and the manifold374. Similar adjustable means is provided by the throttle 370a forthrottling the iluid flow between the annular recess 362 and themanifold 374.

Thus, as the power piston 40 moves down in a return stroke, the returnfluid exhausted from the cylinder 10 is throttled by the throttle 370,the valve 376 being adjustable yto control the rate of the returnstroke. Fluid introduced by the power pump 22 to the valve during thereturn stroke is independently throttled by the throttle 370a to controlthe load on the pump. Y

In the second embodiment, the ball 202 of a pressurerelieving means,similar to that in the rst embodiment, is adapted to seat on the seat204 to close an alternate passage from the inlet port 306 to themanifold 374. The alternate passage in this embodiment includes the port206, which joins an annular recess 307. Referring to.y FIGURE 7, Vtheannular Vrecess 307 is coupled to the manifold 374 by a connecting port309. As previously explained, the manifold 374 connects to the returnport 310.

In operation, excessive fluid pressure in the inlet port 306 forces theball 202 olf the seat 204. Fluid then ilows through the aforementionedpath to the return Vport 310. When the pressure subsides, the spring 212will urge the ball 202 back to the seated position. It will be notedthat the pressure-relieving means is operable in the system during boththe power Stroke and the return stroke of the power piston 40. Duringthe power stroke, the inlet port 306 is in communication with the outletport 308 through the chamber 302. During the return stroke, the inletport 306 and the outlet port 308 remain in communication, but suchcommunication is through the manifold 374 and the ports 375 and 375a andthe respective annular recesses 356 and 362 in the chamber 302.

To recapitulate the operation of the second embodiment, at the end ofthe power stroke iiuid pressure is introduced to the chamber 302 fromthe cylinder 10 through a starting control port 340 having a check valve341 therein and a holding control port 346. Such iiuid moves the spool304 to its second operating position, the movement being yieldinglyopposed by the spring 316, which normally urges the spool 304 to thefirst operating position. The control ports 340 and 346 correspond tothe control ports 1196 and 198 of the first embodiment, and further,shifting the spool 304 between operating positions is accomplished inthe same manner as previously described. Therefore, the description of acycle of operation is not repeated with respect to the secondembodiment.

As spool 304 moves from its second toward its first operating position,control fluid trapped in the end of the chamber 302 bleeds out throughthe restricted passage 336 to the bore 334 and thence through thelateral restricted passage 338 to the annular space 339. Referring tothe drawings, it will be noted that annular space 336 is in constantcommunication with the return port 310. Thus, the control fluid ywill bebled back to the system.

In connection with the shifting of the spool 394 between operatingpositions, it is desirable to have the reversing of the valve besomewhat gradual in order that the System is not subjected to violentsurges of pressure. To preclude such surges of pressure, the lands 352and 356 are formed with tapered surfaces.

The land 352 has reversely tapered surfaces 390 and 391, whichalternately move into longitudinal alignment with an annular recess 392as the spool is moved between first and Second operating positions. Itis noted that the recess 392 is an extension of the outlet port 398, itsfunction being to insure uniform distribution of fluid about the spool304. As the land 352 moves into and out of alignment with the recess392, the passage of fluid between the chamber 302 and the outlet port308 will be gradually blocked or unblocked.

Similarly, the land 360 is formed with a tapered surface 393. As theland 360 is moved into and out of alignment with the annular recess 362,the passage of fluid between the chamber 302 and the recess is graduallyblocked and unblocked.

Although certain embodiments of the invention have been shown anddescribed in considerable detail, it will be understood that variouschanges in the details of construction and arrangement may be madewithout departing from the spirit and scope of the invention as definedin the appended claims.

We claim:

l. In a fluid pressure responsive system of the type wherein a controlelement is selectively moved between alternate positions in response tofluid pressure from at least two separate pressure-sensing sources, anactuator for said element comprising: an expansible chamber having awall movable therein between a first operating position wherein saidchamber is in a contracted condition and a second operating positionwherein said chamber is in an expanded condition, said wall beingoperatively connected to said element and movable therewith at least tothe extent that the first and second operating positions of said wallcorrespond to the alternate positions of said element; starting andholding fluid oonneetions in said chamber adapted to connectrespectively, to said pressure-sensing sources; and means operativelyassociated with the movable wall to block said holding connection whenthe movable wall is in said first operating position and to unblock saidholding connection responsive to movement of said Wall toward saidsecond operating position, whereby control fluid initially admitted tosaid chamber through said starting connection moves said wall towardsaid second operating position to expand said chamber and unblock saidholding connection.

2. In a fluid pressure responsive system of the type wherein a controlelement is selectively moved between alternate positions in response tothe fluid pressure at pressure-sensing sources, an actuator for saidelement comprising: an expansi'ble chamber having a movable Walltherein, said wall being movable in said chamber between a firstoperating position wherein said chamber is in a contracted condition anda second operating position wherein said chamber is in an expandedcondition; means operatively connecting said w-all and said elementwhereby movement of said wall between said first -and second operatingpositions effects movement of said element between its alternatepositions; starting and holding iiuid connections adapted to connectrespectively, to said pressure-sensing sources; means connected to saidmovable wall to block said holding connection when `the wall is in saidfirst operating position and to unblock said holding connection whenIthe wall is moved toward said second operating position, wherebycontrol fluid admitted to said chamber through said starting connectionmoves said wall toward said second operating position to expand saidchamber and unbloek said holding connection and fluid admitted throughsaid holding connection holds said wall in said second operatingposition; and means responsive to the exhaustion of control fluid fromsaid chamber for returning said wall to said' first operating position.

3. In a fluid pressure responsive system of the type wherein a controlelement is selectively moved between alternate positions in response tothe fluid pressures at pressure-sensing sources, an actuator for saidelement comprising: an expansible chamber having a wall mov able thereinbetween a contracted and an expanded posision, said wall beingoperatively connected to said element to move the same as aforesaid; astarting fluid oonneetion adapted to connect one of saidpressure-sensing sources to said chamber for admitting control fluidthereto for moving said wall from said contracted position toward saidexpanded position; ya holding fluid connection adapted to connectanother of said pressure-sensing sources to said chamber at a pointspaced from said starting connection for admitting Ifluid to saidchamber to hold said wall insaid expanded position; means operativelyassociated with said wall to block said holding connection when the wallis in saidcontracted position and to unblock said holding connectionupon movement of the wall toward said expanded position; means forming ableed passage from said chamber for exhausting control fluid therefrom,thereby allowing said wall to move from said' expanded to saidcontracted position so as to block said holding connection; and meansyieldingly urging said wall toward` said contracted position.

4. -A fluid pressure actuated valve system comprising, in combination: atwo-position valving member; an actuator having a pressure responsiveelement movable between first and second limit positions and operativelyconnected to said member to move said member alternately between its twopositions; pressure-sensing sources for supplying fluid for moving saidelement as aforesaid; a starting connection adapted to connect one ofsaid pressure-sensing sources to said actuator for admititng fluid tosaid actuator to move said element toward said' second limit position; aholding connection adapted to oonnect another of said pressure-sensingsources to said actuator at a point spaced from said starting connectionfor admitting fluid to said actuator upon movement of said element fromsaid first toward' said second limit posirtion; means operativelyassociated with said element to block said holding connection when saidelement is in said first limit position and to unblock saidlast-mentioned connection upon movement from said first toward saidsecond limit position; unidirectional flow control means between saidstarting connection and its respective pressure-sensing source forpreventing the exhausting of fluid from said actuator through saidstarting connection, whereby fluid admitted to said actuator throughsaid holding-connection holds said element in said second limit positionirrespective of the pressure in said one of said pressure-sensingsources; means forming a bleed passage from said actuator for exhaustingfluid therefrom; and means responsive to the exhaustion of fluid fromsaid chamber for moving said element to said first position.

5. A fluid pressure actuated valve system comprising, in combination: avalving member movable between an open and a closed position; anactuator having a pressure responsive element operatively connected tosaid member and movable between a first operating position, wherein saidmember is in its closed position, and a second operating position,wherein said member is in its open position; at least two separatesources of fluid pressure, each being vindependently sufficient to movesaid element as aforesaid; respective starting and holding connectionsadapted to connect said pressure sources respectively, to separatepoints in said actuator; and means operatively associated with saidelement to block said holding connection when said element is in saidfirst operating position and to unblock said holding connection uponmovement toward said second operating position, said means beingarranged relative to said valve member whereby the unblocking of saidholding connection occurs prior yto said member reaching its openposition.

6. A reversing valve comprising, in combination: a body having `aninternal chamber with an inlet port, an outlet port, and a return portall communicating with said chamber, and an alternate passage betweensaid inlet port and said return port; a valving member mounted in saidchamber and movable therein between iirst and second operatingpositions, said valving member being operable in said first position toblock llow through said return port, there being constant communicationbetween said inlet and outlet ports during said blocking, and in thesecond position to permit tlow through said return port; valve means insaid alternate passage normally closing said passage, said valve meansbeing responsive to a pressure of a predetermined level to open saidpassage; and means yieldingly urging said valve means to close saidalternate passage.

7. A hydraulic reciprocating motor comprising, in combination: acylinder; a slidable piston in said cylinder adapted to reciprocate overav predetermined path therein in a power stroke and in a return stroke;a power conduit connected to said cylinder adjacent a rst end of saidpath for admitting pressurized fluid to said cylinder to move saidpiston in the power stroke and for exhausting hydraulic fluid from saidcylinder to allow the piston to move in the return stroke; a valve'bodyhaving formed therein -a chamber, connector means at a given pointninsaid chamber in constant communication with said cylinder and powerconduit, and a return port longitudinally displaced in said chamber fromsaid connector means, said return port being adapted to communicatethrough said chamber with said connector means; a valve element slidablydisposed in said chamber for movement between rst and second operatingpositions, said valve element being operable in said first operatingposition t block said return port, and in said second operating positionto open said return port to permit fluid from said connector means tollow through said return port; an actuating plunger in said chamberadjacent one end thereof and operatively associated with said valveelement and movable therewith, -atleast to the extent that the rst andsecond operating positions of said valve element correspond to first andsecond limit positions respectively, of said plunger; a starting conduitconnected at one end to said cylinder adjacent a second end of saidpath, and at the other end to the end of said chamber adjacent saidplunger, whereby pressurized fluid from said cylinder enters saidchamber substantially coincidentally with the termination of the powerstroke to move said spool from its rst toward its second operatingposition; and a holding conduit conne-cted at one end to said cylinderadjacent the lower end thereof, and at the other end to said chamber ata point therein, spaced `from said end of the chamber, said connectionof said holding conduit to said chamber being blocked by said plungerwhen in its rst limit position and being unblocked as said plunger movesfrom said first toward said second limit position, said unblockingoccurring prior to the opening of the return port, whereby fluidadmitted to said chamber through said holding conduit urges said plungerto its second limit position and maintains it therein during the returnstroke.

8. A hydraulic reciprocating motor comprising, in combination: -acylinder; a slidable piston in said cylinder adapted to reciprocate overa predetermined path therein in a power stroke and in a return stroke; apower conduit connected to said cylinder adjacent a ilrst end of saidpath for admitting pressurized lluid to said cylinder to move saidpiston in the power stroke and for exhausting hydraulic iluid from saidcylinder to allow the piston to move in the return stroke; a valve bodyhaving formed therein a chamber, connector means at a given point insaid chamber in constant communication with said cylinder and powerconduit, and a return port longitudinally displaced in said chamber`from said connector means, said return port being adapted tocommunicate through said chamber with said connector means; a valveelement slidably disposed in said chamber for movement between first andsecond operating positions, said valve element being operableV in saidtirst operating position to block said return port, and in said secondoperating position to open said return port to permit fluid from saidconnector means to tlow through said return port; an actuating plungerin said chamber adjacent one end thereof and operatively associated withsaid valve element -to move the same as aforesaid between correspondingtlirst and second positions; a starting conduit connected at one end tosaid cylinder adjacent a second end of said path, and at the other endto the end of said chamber adjacent said plunger, whereby pressurizediluid from said cylinder enters said chamber through said startingconduit and -acts on said plunger substantially coincidentally with thetermination of the power stroke to move said plunger-,toward 4its secondposition; a holding conduit` connected -at one end to said cylinderadjacent the first end of said path, and -at the other end to saidchamber at a point therein, spaced from said end of the chamber, saidconnection of said holding conduit to said chamber being blocked by saidplunger in its first position and unblocked upon movement of saidplunger toward its second position, whereby `fluid initially admitted tosaid chamber through said starting conduit moves said plunger tounblocksaid holding connection and iluid admitted tov said chamber through saidholding conduit holds said plunger in its second position during thereturn stroke; and means for exhausting fluid from said chambersubstantially coincidentally with the termination of the return stroketo permit said plunger to move from its second toward its firstposition.

9. A hydraulic reciprocating motor comprising, in combination: avertical cylinder; a slidable piston in said cylinder adapted toreciprocate therein in a power and a return stroke; la power conduitconnected to said cylinder adjacent the lower end thereof for ladmittingpressurized tluid to said cylinder to move said piston in the powerstroke and for exhaustinghydraulic fluid from said cylinder to allow thepiston to move in the return stroke; a.- valve body having formedtherein a chamber, connector means at a given point in said chamber inconstant communication with said cylinder and power conduinand a returnport longitudinally displaced in said chamber from said connector means,said return port being adapted to communicate through said chamber withsaid connector means; a valve element slidable disposed in said chamberfor movement between first and second operating positions, said-valveelement being operable in said first operating position to block saidreturn port, and in said second operating position to open said returnport to permit fluid from said connector means to ilow through saidreturn port; an actuating plunger in said chamber adjacent one endthereof and operatively associated with said valve element and movabletherewith, at least to the extent that the ilrst and second operatingpositions of said valve element correspond to first and second limitpositions respecu'vely, of said plunger; a starting conduit connected atone end to said cylinder adjacent the upper end thereof, and at theother end to the end of said chamber adjacent said plunger, wherebypressurized fiuid from said cylinder enters said chamber through saidstarting con-- duit substantially coincidentally with the termination ofthe power stroke to move said plunger from its irst toward its secondlimit position; and a holding conduit connected at one end to saidcylinder adjacent the lower end thereof, and at the other end to saidchamber at a point therein, spaced from said end of the chamber, saidconnection of said holding conduit to said chamber being blocked by saidplunger when in its first limit position and -being unblocked as saidplunger moves from said first toward said second limit position, wherebyfluid admitted to said chamber through said holding conduit holds saidplunger in said second limit position during the return stroke.

l0. A hydraulic reciprocating motor comprislng, 1n combination: avertical cylinder; a slid'able piston in said cylinder adapted toreciprocate therein in a power and a return stroke; a power conduitconnected to said cylinder adjacent the lower end thereof for admittingpressurized uid to said cylinder to move said piston in the power strokeand for exhausting hydraulic uid from said cylinder to allow the pistonto move in the return stroke; a valve body having formedtherein achamber, connector means at a given point in said chamber in constantcommunication with said cylinder and power conduit, and a return portlongitudinally displaced in said chamber from said connnector means,said return port being adapted to communicate through said chamber withSaid connector means; a valve element slidably disposed in said chamberfor movement ybetween rst and second operating positions, said valveelement being operable in said tirst operating position to block saidreturn port, and in said second operating position to open said returnport to permit fluid from said connector means to iiow through saidreturn port; an actuating plunger in said chamber adjacent one endthereof and operatively connected to said valve element and movabletherewith, at least to the extent Ithat the `first and second operatingpositions of said valve element correspond to iirst and second limitpositions respectively, of said plunger; a starting conduit connected atone end to said cylinder adjacent the upper end thereof, and at theother end to the end of said chamber adjacent said plunger, saidconnection to said cylinder being suiciently spaced from the top thereofto allow said piston to move above said last-mentioned connection at theend of the power stroke, whereby pressurized iiuid from said cylinderbelow said conduit acts on said plunger to move it toward said secondlimit position; a holding conduit connected at one end to said cylinderadjacent the lower end thereof, and at the other end to said chamber ata point therein, longitudinally spaced from said end of the chamber,said connection of the holding conduit to said cylinder being spaced4above said connection to said power conduit lby a distance greater thanthe length of said piston, said connection of said holding conduit tosaid chamber being blocked by said plunger when in its first limitposition 4and being unblocked upon movement of the plunger toward itssecond limit position, whereby fluid admitted to said chamber throughsaid holding conduit moves said plunger to its second limit positionirrespective of tiuid admitted through said starting conduit andmaintains said plunger therein during the return stroke of the powerpiston; unidirectional ow control means in said starting conduitpreventing the exhaustion of fluid from said chamber through saidstarting conduit; means for exhausting iiuid from said chambersubstantially coincidentally with the termination of said return stroketo permit said plunger -to move from its second to its first limitposition; and means yieldingly urging said plunger toward said irstlimit position.

1l. A hydraulic reciprocating motor comprising, in combination: aventical cylinder; a shdable piston in said cylinder adapted toreciprocate therein in a power and a return stroke; a power conduitconnected to said cylinder adjacent the lower end thereof for admittingpressurized iiuid to said cylinder to move said piston in the powerstroke and for exhausting hydraulic fluid from said cylinder to allowthe piston to move in the return stroke; a valve body having formedtherein, a cylindrical chamber, connector means tat. a given point insaid chamber in constant communication with said cylinder and powerconduit, and a return port longitudinally displaced in said chamber fromsaid connector means, said return port being adapted to communicatethrough said chamber with said connector means; a spool slidablydisposed in said chamber for movement between rst and second operatingpositions, said spool having a land formed thereon which is operable insaid first operating position to block said return port, and in saidsecond operating position to open said return port -to permit fluid fromsaid connector means to how through said return port; an actuatingplunger formed on said spool and slidable in said chamber adjacent oneend thereof in response to uid pressure therein to move said spool asaforesaid; a starting conduit connected at one end to said cylinderadjacent the upper end thereof, and at the other end to the end of saidchamber adjacent said plunger, said connection to said cylinder beingsufiiciently spaced from the top of said cylinder to allow said pistonto move `above said last-mentioned connection at the end of the powerstroke, whereby pressurized huid from said cylinder below said pistonenters said chamber through said starting conduit Aand acts on saidplunger to move said spool toward its second operating position; aholding conduit connected at one end to said cylinder adjacent the lowerend thereof, and at the other end to said chamber at a point therein,longitudinally spaced from said end of the chamber, said connection ofthe holding conduit to said cylinder being spaced above said connectionto said power conduit by a distance greater than the length of saidpiston, said connection of said holding conduit to said chamber being inthe cylindrical wal-l of said chamber and being blocked by said plungerwhen said spool is in its first operating position and being unblockedas said spool moves from its first toward its second operating position,said unblocking occurring prior to opening of said return port, wherebytiuid admitted to said chamber through said holding conduit urges saidspool to its second operating position and maintains it therein duringthe return stroke of said piston; a check valve in said starting conduitpreventing the exhaustion of fluid from said chamber through saidstarting conduit; a bleed passage formed in said plunger for exhaustingiiuid from said chamber at the end of the return stroke to permit saidspool to move from its second to its first operating position, saidbleed passage being of sutiicient size to permit movement of saidplunger to block the connection :to said holding conduit prior tomovement of said piston in said cylinder above the connection to saidholding conduit during the power stroke; and a compression springyieldingly urging said spool to its first operating position.

l2. A reversing valve comprising, in combination: a valve body having aninternal operating chamber with an inlet port, an outlet port, and areturn port, all cornmunicating with said chamber, and an internalactuating chamber; a valving member slidably mounted in said operatingchamber for movement between tirst and second operating positions, saidmember being operable in said iirst operating position to block saidreturn port, there being constant communication between said inlet andoutlet ports during said blocking, and in said second operating positionto open said return port to permit iiuid flow from said inlet and outletports through said return port; a pressure responsive element in saidactuating `chamber and movable therein between rst and second limitpositions, said element being operatively associated with said valvingmember and movable therewith, at least to the extent that the first andsecond limit positions of said element correspond to the first andsecond operating positions, respectively, of said valving member; meansforming a starting port in said body in constant communication with saidactuating chamber, said starting port being adapted to admit pressurizedcontrol flow to said actuating chamber to move said element toward itssecond limit position; means forming a holding port in said bodycommunicable with :said actuating chamber `at a point spaced from saidstarting port, said holding port being adapted to admi-t pressurizedcontrol uid to said actuating chamber upon movement of said element fromits rst to its second limit position; and means on said element blockingsaid holding port when said element is in its rst limit position landunblocking said holding port upon movement from its lirst to its secondlimit position, said iunblocking occurring prior to the opening of saidreturn port.

13. A reversing valve comprising, in combination: a body having formedtherein, an internal chamber with the inlet port, an outlet port, and areturn port, there being provided a first uid passage between lsaidinlet port and said return port through said chamber and a second fluidpassage between said outlet port and said return port through saidchamber; a valving member slidably mounted in said 'chamber and movabletherein between rst and second operating positions, 'said member beingoperable in said first operating position to block fiow through saidfirst and second passages, there being constant communication betweensaid inlet and outlet ports through said chamber during `said blocking,and in said seco-nd operating position to open said passages for fluidflow Itherethrough; and rst and second adjustable throttles mounted insaid body and operable in said 18 rst and second passages, respectively,to throttle the Huid How.

14. A fluid pressure actuated valve system comprising, in combination: atwo-position valving mem-ber; an vactuator having a uid pressureresponsive element movable from a first to a second operating positionand operatively associated with lsaid member to move it from one to ktheother of its two positions; two separate sources of uid pressure, eachbeing independently sufficient to move said element as aforesaid; a pairof connections adapted to connect said pressure sources, respectively,to separate points in said actuator; and means on said element operablein the rst operating position in said element to block one of saidconnections and during movement of said element from said tnst to saidsecond operating position lto unbock said one of said connections, saidunblocking occurring prio-r to said valving member moving tothe other ofits positions.

References Cited in the le of this patent UNITED STATES PATENTS2,156,326 Wineman May 2, 19'39 2,852,001 Andrews Sept. 16, 19582,887,093 Jones May 19, 1959 2,914,037 Johnston Nov. 24, 1959'

